Radioactive radiation dosimeter of the silver phosphate glass type



y 8, 1968 R G. BRYER 3,385,968 I RADIOACTIVE RADIA'fION DOSIMETER OF THESILVER PHOSPHATE GLASS TYPE Filed Jan. 18, 1966 10 15 10b 70a 4 I '3 I30v \l I FIG. 2.

. ATTORNEY United States Patent 3,385,968 RADIOACTIVE RADIATIONDOSIMETER OF THE SILVER PHOSPHATE GLASS TYPE Robert George lBryer,Rnislip, England, assignor to R. A.

Stephen & Company Limited, Mitcham, Surrey, England, a limited companyof the United Kingdom Continuation-impart of application Ser. No.282,039, May 21, 1963. This application Jan. 18, 1966, Ser. No. 521,284Claims priority, application Great Britain, May 21, 1962, 19,462/ 62 2Claims. (Ci. 250-83) The present application is a continuation-in-partapplication of co-pending application Ser. No. 282,039 filed May 21,1963, now abandoned.

This invention relates to dosimeters of the locket type, for personalwear. The invention has for its object to provide an improved formthereof.

The invention is particularly applicable to a locket type dosimeter ofthe non-direct reading type. In such a dosirneter there is used anelement of radiation-sensitive material, the effect of radiation uponwhich is not directly observable, so that the element must be examinedby a separate reading means to ascertain the degree of radiation towhich it has been subjected. An example of such a material having thedesired properties is a glass containing a dissociable phosphatematerial, such as silver phosphate. In practice it is required to removeor expose the element in the reader, and so it is necessary that theelement should be mounted in a manner to afford repeated and readyaccess to it.

With certain materials of this class, such as the glass mentioned above,it is necessary also to provide an adequate seal for the material whenin use. The reason for this is that if the element is mounted with freeaccess to the air, it may occur that the phosphate material willdissociate without being irradiated and will then give rise to aninaccurate indication. Also, with silver phosphate it may occur thatthere is superficial oxidization of the silver, producing a surface filmwhich affects the light or radiation transmission of the glass. As it isnecessary to read the dosimeter by means which depend upon the lighttransmission of the glass, the production of such a silver oxide willalso lead to an inaccurate indication.

The present invention has for its object to provide a dosimeter locketwhich provides an adequate seal for the element, and which can bereadily and repeatedly opened for reading.

The invention includes a dosimeter including a radiation-sensitiveelement, a casing for sealing said element, said casing being adapted tobe opened at will to give access to said element, said casing includingtwo separable parts and a resilient sealing member engaged betweenadjacent surfaces of said parts, said surfaces lying about an accessopening, and a housing for receiving said casing and for imposingsealing pressure on said surfaces, said housing having two portionsrespectively engaging said casing parts and being relatively rotatablefor imposing said pressure on said surfaces, at least one of said partshaving localized engagement with its associated housing portion, wherebyto permit rotation relative thereto.

The inner casing is made of steel, brass or a like metal which, unlikeplastic materials, will not allow to any great extent the passage bydiffusion of gases or vapors into the inner casing, will not produceemanations of a derogatory nature in the gas-containin g enclosure, andwill not deform with age or temperature. It has been found that the onlymetal which diffuses gases much more readily than plastic is palladium.This metal is of course much too expensive to consider for use indosimeters.

In one convenient construction of the device for read- "ice ing theelement, the same is subjected to radiation directed upon it from afirst direction, and the desired indication obtained as a function of aradiation, such as one of different wavelength, emerges from the elementin a second direction, at an angle, preferably a right angle, to thefirst. This requirement means that the element must be readily removablefrom the locket to enable the desired reading to be made, oralternatively, the element must be so accommodated in the locket as toenable this to be done. In a preferred form of the invention describedhereinafter, a locket is provided which can be located, while in itsnormally closed condition, in a reader and then by a simple action theelement can be exposed for reading, remaining located in the reader.

Further features and advantages of the invention will be apparent fromthe following description of an embodiment thereof, given, by way ofexample in conjunction with the accompanying drawings, in which:

FIG. 1 is a half plan view of a locket; and

FIG. 2 is a medial section through the locket.

This locket comprises an outer casing 10 suitably made of a moldedsynthetic plastic material and having a central recess 11 whichaccommodates a lead shield 12 and an inner casing 13 of metal. The leadshield 12 is located on casing 10 by means of an annular projection 10aformed integrally with casing 10 and engaging in a central opening 14 inthe shield 12. The casing 13, and with it the shield 12, are securedagainst axial movement relative to casing 10 by a pin 15 attached toinner casing 13 and passing through outer casing 10 into a recess 10b,the pin being held, for example, by deforming its free end over a washer16, or alternatively by a spring ring engaging in a groove formed in thepin. For reasons that will appear later in the description, the casing13 is free to rotate. The portion 10c of casing 10 defining the openingto the recess 11 is screw-threaded to receive a lid 17 having ascrewthreaded peripheral portion 17a. Supported on lid 17 are a leaddisk 18 and an inner casing lid 20; the outer edge 20a of lid 20 isdepressed as shown and fits within an annular recess 17b of the lid 17and thus provides a receptacle for a sealing O-ring 21. O-ring 21cooperates with a flanged outer edge 13a of the casing 13 to provide acompletely sealed enclosure between inner casings 13 and 20 when the lid17 is screwed into the access opening of casing 10. For clarity ofillustration, a rather large gap is shown between flanged edge 13a andcasing 20. In practice this gap will be very small or nonexistent, sinceduring assembly O-ring 21 is deformed until edge 13a and casing 20 comein contact with each other.

The seal which is formed by O-ring 21 does not prevent gases fromdiffusing into the inner casing, but it occupies a minute fraction ofthe total surface area of the inner casing, and accordingly, the amountof gases which can diffuse through the seal is minute and negligible forall practical purposes.

Within the enclosure there is accommodated, by means of a clip fasteningnot shown, a small block 22 of glass which contains silvermetaphopshate. The lead shields 12 and 18 may have in them perforationsof suitable size in order to equalize the response of the glass 22 todifferent energy levels.

The outer casing 10 also has an integrally formed projection 10dprovided with a hole 25 for supporting cord or the like.

Holes 23 in lid 17 enable the locket to be located, unopened, oncorresponding locating pins in the reader; the casing 10 is thenunscrewed from the lid 17 without the use of a separate tool, leavingthe glass block exposed for reading in the manner previously described.

Instead of screw-threaded engagement between casing 10 and lid 17, thecasing 10 may be formed with an interrupted groove or grooves which canreceive projections formed on the peripheral portion of the lid 17 whenit is angularly rotated with respect to the casing 10.

With the construction described, the glass 22 is completely sealed andis thereby protected against contamination by the atmosphere, or againstany migration of a constituent of the casing 10 or its lid 17; operationof the dosimeter is thereby stabilized over long periods.

Further, by making the inner casing 13 rotatable, objectionable rubbingbetween the O-ring 21 and flange 13a, when the lid 17 is being screwedinto or out of the casing 10, is eliminated; the casing 13 being free torotate with the lid 17.

While the invention has been described in detail with respect to acertain now preferred example and embodiment thereof, it will beunderstood by those skilled in the art, after understanding theinvention, that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention, and it isintended, therefore, to cover all such changes and modifications in theappended claims.

What is claimed is:

1. A portable dosimeter comprising in combination:

(a) a casing made of a gas diffusion pervious material and having agenerally cup-shaped bottom part and a lid screwable into the rim of thebottom part;

(b) an inner casing made of a substantially gas impervious material andhaving an imperforate generally cup-shaped bottom part nested in theouter casing bottom part and an imperforate lid fitted between the lidof the outer casing and the peripheral rim of the bottom part of theinner casing, said rim terminating in an outwardly extended flange andsaid inner casing lid having a set-off peripheral rim disposed inparallel superimposition with said flange spaced apart therefrom todefine an annular space between said flange and said rim;

(0) a sealing ring fitted in said space, sealing pressure beingapplicable to the ring by screwing the outer casing lid into the outercasing bottom part;

((1) a substantially imperforate cup-shaped lead shield interposed'between said two casing bottom parts;

(e) a substantially disc-shaped imperforate lead shield interposedbetween two lids; and

(f) a radiation-sensitive element disposed within said inner casing.

2. A dosimeter according to claim 1, wherein said cup-shaped shield hasan aperture, and comprising fastening means securing said bottom partsto each other and extending through said aperture.

References Cited UNITED STATES PATENTS 2,415,031 1/1947 Kuhn et al.220-46 2,580,057 12/1951 Wilhelm 220-46 X 2,879,914 3/1959 Fleckenstein220-46 X 3,042,802 3/1962 Just et al. 250-83 3,100,262 8/1963 Shenker etal. 25083 2,750,515 6/1956 Shurcliff 250-83 ARCHIE R. BORCHELT, PrimaryExaminer.

1. A PORTABLE DOSIMETER COMPRISING IN COMBINATION: (A) A CASING MADE OFA GAS DIFFUSION PREVIOUS MATERIAL AND HAVING A GENERALLY CUP-SHAPEDBOTTOM PART AND A LID SCREWABLE INTO THE RIM OF THE BOTTOM PART; (B) ANINNER CASING MADE OF A SUBSTANTIALLY GAS IMPERVIOUS MATERIAL AND HAVINGAN IMPERFORATE GENERALLY CUP-SHAPED BOTTOM PART NESTED IN THE OUTERCASING BOTTOM PART AND AN IMPERFORATE LID FITTED BETWEEN THE LID OF THEOUTER CASING AND THE PERIPHERAL RIM OF THE BOTTOM PART OF THE INNERCASING, SAID RIM TERMINATING IN A OUTWARDLY EXTENDED FLANGE AND SAIDINNER CASING LID HAVING A SET-OFF PERPHERAL RIM DISPOSED IN PARALLELSUPERIMPOSITION WITH SAID FLANGE SPACED APART THEREFROM TO DEFINE ANANNULAR SPACE BETWEEN SAID FLANGE AND SAID RIM; (C) A SEALING RINGFITTED IN SAID SPACE, SEALING PRESSURE BEING APPLICABLE TO THE RING BYSCREWING THE OUTER CASING LID INTO THE OUTER CASING BOTTOM PART;